Method of manufacturing fin metal tubing

ABSTRACT

An ordinary cylindrical metal tube is formed into an intermediate tubing having thicker wall portions at which fins are to be formed subsequently, and the intermediate tubing is then subjected to a cold drawing operation by using a finlike die and a cylindrical plug so as to form fins from the thicker wall portions.

United States Patent Inventors Masaharu Odaki;

Takashi Konno; Tatsuya Mochizuki; Osamu Nakahara; Makoto l-lashimoto, all of Kawasaki-shi, Japan Appl. No. 840,249 Filed July 9, 1969 Patented Dec. 28, 1971 Assignee Nippon Kokan Kabushiki Kaisha Priority July 13, 1968 Japan 43/48845 METHOD OF MANUFACTURING FIN METAL TUBING 10 Claims, 18 Drawing Figs.

US. Cl 72/278, 72/283, 72/276, 29/1573 A, 113/118 A Int. Cl B21c 1/04, B2ld 53/02 [50] Field of Search 72/283, 276, 278, 274, 469; 29/1573 A, 157.4; 80/623; 1 13/118 A [56] References Cited UNITED STATES PATENTS 721,209 2/1903 Mannesmann 29/1573 3,327,513 6/1967 Hinshaw 72/283 FOREIGN PATENTS 623,313 10/1962 Belgium 72/283 Primary Examiner-Charles W. Lanham Assistant Examiner-Michael .l. Keenan Attorney-Flynn & Frishauf ABSTRACT: An ordinary cylindrical metal tube is formed into an intermediate tubing having thicker wall portions at which fins are to be formed subsequently, and the intermediate tubing is then subjected to a cold drawing operation by using a finlike die and a cylindrical plug so as to form fins from the thicker wall portions.

PATENTEUnEc28|9n 3630 062 SHEET 1 OF 4 PATENTEUUEC28I97| $530,052

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SHEET 0F 4 9 (A) F|G.9 (8) FIG IO (B) FIG. IO (A) BACKGROUND OF THE INVENTION This invention relates to a method of manufacturing fin metal tubing and more particularly to an improved method of cold drawing from hot-rolled tubing with special plug.

Among prior methods of manufacturing fin metal tubing are included:

1. a method utilizing a hot extrusion process,

2. a method utilizing a plug mill process,

3. a method wherein a fin tubing manufactured by the method of either (I) or (2) is cold drawn again,

4. a method wherein a flat bar is welded into a metal tube.

The method utilizing a hot extrusion machine and the method utilizing a plug mill are not always satisfactory in that the dimensional accuracy and surface quality of the products are not uniform. Whereas the method (3) wherein fin tubing produced by either method 1) or (2) are further subjected to the cold drawing operation can provide products of excellent quality or having excellent dimensional accuracy and improved inner and outer surface finish, this two step method increases the cost of manufacturing. Further, in the method wherein a flat bar or bars are welded into a cylindrical tube the heat of welding affects the metallurgical or physical properties of the tube.

In order to solve these difficulties there has been proposed a method of manufacturing fin tubes wherein an ordinary cylindrical metal tube is code drawn by utilizing a finlike die. More particularly, a fin tubing 2 as shown in FIG. 1A may be manufactured by cold drawing an ordinary cylindrical metal tube 3 shown in FIG. 13 with a die 5 having grooves 4 corresponding to fins 1 (see FIG. 1C) and a cooperating cylindrical plug, not shown. It is, however, well known that there is formed some depressions 6 at the opposite wall of each fin formed by the above prior art method, as shown in FIG. 1D.

SUMMARY OF TIIE INVENTION It is therefore an object of this invention to provide a new and improved method of manufacturing a fin metal tubing without the accompanying difficulties mentioned above.

According to this invention an ordinary cylindrical metal tube is formed into an intermediate tubing having thicker wall portions at which fins are to be formed subsequently, and the intermediate tubing is then subjected to a cold drawing operation by using a finlike die and a cylindrical plug so as to form fins from said thicker wall portions.

BRIEF DESCRIPTION OF THE DRAWING FIG. IA is a cross-sectional view of a fin metal tubing,

FIG. 1B shows a cross section of a circular tube,

FIG. 1C shows a cross section of a finlike die utilized to manufacture a fin tubing from the cylindrical tube shown in FIG. 1A;

FIG. 1D shows a cross section of a prior art fin tubing produced by utilizing the finlike die shown in FIG. 1C and the tube shown in FIG. 18;

FIG. 2 shows a longitudinal sectional view of the apparatus employed in the first step of the cold drawing process embodying this invention;

FIG. 3 shows a cross section taken along a line III-III IN FIG. 2;

FIG. 4 shows a cross section of an intermediate tubing;

FIG. 5 shows a longitudinal sectional view of the apparatus utilized in the second step of this invention;

FIG. 6 shows a cross section taken along a line VIVI in FIG. 5;

FIGS. 7(A), 7(B), 8(A), 8(8) and 9(A), 9(B) show cross sections of the intermediate product and of the final product of a modified embodiment and;

FIGS. 10(A) through (.C) show a sectional view to illustrate typical dimensions of the product. DETAILED DESCRIP- TION OF THE PREFERRED EMBODIMENTS In accordance with this invention, to provide a fin metal tubing 2 as shown in FIG. I, an ordinary cylindrical metal tube 3 as shown in FIG. 1B is subjected to a cold drawing operation by utilizing a plug 7 having rectangular or elliptical cross section as shown in FIGS. 2 and 3 and a die 8 of circular cross section, instead of a plug of circular cross section, so as to obtain an intermediate tubing 9 having a nonuniform wall thickness. As shown in FIG. 4, the tubing 9 has thicker wall portions 10 which are to be utilized to form fins as described later.

The tubing 9 is then utilized as an intermediate tubing and subjected to a cold drawing operation by employing a finlike die 5 having a required configuration as shown in FIG. 1C, for example, and a cylindrical plug 11, as shown in FIG. 5 so as to readily produce a fin tubing as shown in FIG. 1A which is free from any internal depressions (see FIG. ID).

FIG. 7B shows a cross section of a fin metal tubing having four equally spaced-apart radial fins and FIG. 7A shows an intermediate tubing to obtain this product. Similarly, FIG. 8B shows a cross section of a modified fin metal tubing having two spaced-apart radial fins and FIG. 8A shows a cross section of an intermediate tubing suitable for producing the product shown in FIG. 88. FIG. 9 shows a cross section of a modified intermediate tubing in which diametrically opposing portions thereof corresponding to the fins of the finished products are bulged radially inwardly as well as outwardly.

FIG. 10 illustrates typical dimensions of a mother tube A, an intermediate tube B after the first step and a product C after the second step. These dimensions are:

Mother tube A:

outer diameter 89.l mm. wall thickness 10 mm. Intermediate tubing 8:

Outer diameter 76.3 mm.

wall thickness of thinner portions 7 mm. wall thickness of thicker portions l0 mm. Product C:

Outer diameter 63.5 mm. wall thickness 5.2 mm. fin thickness 6.0 mm. width of the fin 7L5 mm.

Thus, in accordance with this invention, a less expensive ordinary cylindrical tube is utilized as a mother tube. The mother tube is subjected to a special deformation step by means of which portions of an intermediate tube, at which fins are to be formed subsequently, are thickened. In this manner, the forming flow of the material at the fins is enhanced. It is possible to provide, with ease, a fin metal tubing free from internal depressions and having accurate configuration and dimensional accuracies as well as excellent surface finish. Moreover, the manufacturing cost of using this invention is low because the cost of the starting material is low and because a conventional cold drawing machine can be used.

In addition to the illustrated fin metal tubings, this invention can also provide some fin metal tubings having radial fins directed in a number of directions, having one-side twodirection fins or having many other configurations, which is suitable for use in boilers and for structural purposes. Further, it is to be understood that intermediate tubing can also be readily manufactured by a cold pilger roll and the like.

While the invention has been described in terms of preferred embodiments thereof, many changes and modifications thereof will be obvious to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

I. A method of manufacturing a fin metal tubing comprisforming an intermediate tubing from a cylindrical metal tube, said intermediate tubing having thicker wall portions at the locations corresponding to where fins are to be formed in a subsequent step; and

cold drawing said intermediate tubing through a closed periphery finlike drawing die and a cylindrical plug with the fin-forming openings of said die being in registration with said thicker wall portions of said intermediate tubing, to form fins from said thicker wall portions, said periphery of said drawing die remaining closed throughout said cold drawing step.

2. The method according to claim 1 wherein said intermediate tubing is formed by using a circular die and a plug of noncircular cross-sectional configuration, to thereby produce said thicker wall portions.

3. The method according to claim 2 wherein the cross section of said plug is substantially rectangular.

4. The method according to claim 2 wherein the cross section of said plug is elliptical.

5. The method according to claim 1 wherein the cross section of said intermediate tubing has square longitudinal opening therein.

6. The method according to claim 1 wherein the cross section of said intermediate tubing has a sector shaped longitudinal opening therein.

7. The method according to claim 1 wherein said intermediate tubing has radially inwardly and outwardly bulged portions at said locations corresponding to where said fins are to be formed.

8. The method according to claim 1 wherein the cross section of said intermediate tubing has a rectangular longitudinal opening.

9. The method according to claim 1 wherein said intermediate tubing has a circular outer periphery.

10. The method according to claim 1 wherein said thicker wall portions are located asymmetrically about the periphery of said intermediate tubing to produce asymmetrically located fins.

i l l t i 

1. A method of manufacturing a fin metal tubing comprising: forming an intermediate tubing from a cylindrical metal tube, said intermediate tubing having thicker wall portions at the locations corresponding to where fins are to be formed in a subsequent step; and cold drawing said intermediate tubing through a closed periphery finlike drawing die and a cylindrical plug with the fin-forming openings of said die being in registration with said thicker wall portions of said intermediate tubing, to form fins from said thicker wall portions, said periphery of said drawing die remaining closed throughout said cold drawing step.
 2. The method according to claim 1 wherein said intermediate tubing is formed by using a circular die and a plug of noncircular cross-sectional configuration, to thereby produce said thicker wall portions.
 3. The method according to claim 2 wherein the cross section of said plug is substantially rectangular.
 4. The method according to claim 2 wherein the cross section of said plug is elliptical.
 5. The method according to claim 1 wherein the cross section of said intermediate tubing has a square longitudinal opening therein.
 6. The method according to claim 1 wherein the cross section of said intermediate tubing has a sector shaped longitudinal opening therein.
 7. The method according to claim 1 wherein said intermediate tubing has radially inwardly and outwardly bulged portions at said locations corresponding to where said fins are to be formed.
 8. The method according to claim 1 wherein the cross section of said intermediate tubing has a rectangular longitudinal opening.
 9. The method according to claim 1 wherein said intermediate tubing has a circular outer periphery.
 10. The method according to claim 1 wherein said thicker wall portions are located asymmetrically about the periphery of said intermediate tubing to produce asymmetrically located fins. 